Black and White introduced the Dream World, where Pokemon with different abilities can be caught.
Maybe it is possible to implement a special area in the GBA games where Pokemon will have different abilities. I experimented with the Wally event from RSE.

Quote:

Originally Posted by diegoisawesome

There are four specials in that event you should be aware of: special 0x28, special 0x12F, special 0xA0, and special 0x29. special 0x28 saves your first Pokémon into memory for retrieval later, special 0x12F overwrites your first Pokémon with a specified Pokémon, special 0xA0 is the actual battle, and special 0x29 overwrites your first Pokémon with the one saved in memory.

I was messing around with the event, and deleted special 0x29, which causes that after the event, you still have the Zigzagoon. However, there is something special about this Zigzagoon: it has no ability instead of Pickup.
If we could import a special table that connects every Pokemon with its Dream World ability, and the game then checks when encountering the Pokemon where the player is, and when it's at a special place, the Pokémon will have that ability.
I think all of this is possible by creating and editing ASM routines.
What do you think? Is this a good idea? If you can help, please help. Maybe we could make our very own Dream World!